The invention relates to in-band signaling, and in particular to all-optical cross-connect (OXC) switches providing an in-band signaling capability. Such a switch is often called a transparent OXC because the signals are kept in the optical format. The invention finds application to micro-electromechanical systems (MEMS), but it is not so limited.
The all-optical cross-connect switch promises to become a key element of fiber-optic networks. Steering elements in the optical switch are used to direct beams of light from input fibers to the desired output fibers. The amount of optical power coupled through a given connection is a function of a) the amount of power present in the input fiber, b) insertion losses at the fibers, lenses, and steering elements such as mirrors, c) coupling loss due to mode radii mismatches and longitudinal errors, and d) coupling loss due to errors in beam alignment as effected by the steering elements.
Previous optical switches have not capitalized on the loss due to errors in beam alignment as a means of intentionally modulating the optical power emerging from the output fibers en route to certain other elements of optical network. A fraction of signal power can be utilized to generate a set of commands that instruct the actions of other device elements downstream along the optical path. This command set can be optically encoded as a sequence of events expressed by different optical power levels or discrete frequencies or the combinations. Such in-band signals travel along the same optical channels available for data. One example usage is to embed a command into the optical data channel so the receiving optical switch can use the command to determine what optical connection should be made for the incoming data. Another example is to use the command as a key to decipher the incoming data. In an all-optical network employing optical switches in conjunction with power-level-sensitive elements such as optical amplifier and multi-wavelength systems, the signaling function currently executed using dedicated elements could potentially be absorbed by the optical switch, thereby minimizing or eliminating potentially the need for expensive post-switch signaling sources.
In-band signaling techniques can be implemented with a single mirror actuated with at least one actuator used as a beam-steering element, with the power loss being governed by the mirror deflecting angle in at least one axis away from a set of angles that maximize coupling.
In the prior art such as found in U.S. Pat. Nos. 6,711,340; 6,484,114 and 6,556,285 of the assignee of the present invention Glimmerglass Networks, Inc., techniques were disclosed for optical beam alignment of MEMS based cross-connect switches and the like using a constant amplitude dithering technique. The subject matter of those patents is incorporated by reference herein for all purposes. Although the power-loss mechanism is similar to the loss mechanism employed in the present context, the prior art is not applicable to the general case of using two or more steering elements, or to the specific case of an in-operation optical switch utilizing prescribed motions of the steering elements that prohibit the methods of the prior patents. What is needed is a technique for optical modulation that can be effected using the steering elements of an in-operation optical switch without deleterious impact on the switching functions.